Moving vB/vBseo + joomla CMS into third domain. Pros and Cons.

Ok, in short:
What we have.
1. Community CMS at 1domain.co.nz
2. Community forum at 2domain.net
3. 1domain.com parked at 1domain.co.nz

To improve SEO planing to do:
1. Move CMS Joomla to root of 1domain.com
2. Move community forum to 1domain.com/forum
3. Establish Permanent 301 redirects from old domains to the 1domain.com containing CMS+forum

Technically, it can be done.
Big advantage of doing so will be that everything will be in one domain. Very large site, etc..
Disadvantage i can see is that links between 1domain.co.nz 2domain.net is highly relative in regards to SEO. Moving everything to single domain will certainly missout on this.

Is any other SEO pros and cons to consider?

If your site caters ONLY to those folks in New Zealand (i assume that's the nz country code), I would suggest leaving it on the country code domain.
If not, and your site caters to a GLOBAL topic (or, at least more than just NZ), then moving to the .com is the correct thing to do in my opinion.

Make the .com primary, park the .co.nz on it.
The [How to] Setup www.yourdomain.com or yourdomain.com (www vs. non-www) - With .htaccess 301 redirects - vBulletin SEO Forums redirect will take care of the rest. Integrating the CMS may require a manual effort to 301 content. You may find better info at a Joomla! site. Another thing to consider is to just completely migrate to vb4 and use that as your CMS instead.

Originally Posted by Brian Cummiskey

If your site caters ONLY to those folks in New Zealand (i assume that's the nz country code), I would suggest leaving it on the country code domain.
If not, and your site caters to a GLOBAL topic (or, at least more than just NZ), then moving to the .com is the correct thing to do in my opinion.

Make the .com primary, park the .co.nz on it.
The [How to] Setup www.yourdomain.com or yourdomain.com (www vs. non-www) - With .htaccess 301 redirects - vBulletin SEO Forums redirect will take care of the rest. Integrating the CMS may require a manual effort to 301 content. You may find better info at a Joomla! site. Another thing to consider is to just completely migrate to vb4 and use that as your CMS instead.

Yes, we went global, so .co.nz is not good enough any longer. Comes to the absurd things like that we get rejected from Directories on the base of been sub-domains of .CO.NZ . Never mind.
Separate CMS is very important to us as a main site/page of the portal. Unfortunately vB CMS is very far behind from the CMS's leaders such as Joomla or Drupol.
Believe it or not i think that forum software have nothing to do with CMS or so call "modern social networks". Big mistake of forum software producer is to try to be something of what they are not... Forum software/sites is much more bigger in importance.

Back to the topic.
Is any suggestions in regards to illuminating down time due to domain switches at vBSEO and vB?

I would suggest opening a ticket to have your license moved to your new location, and at the same time ask for a 30-day test license on the current domain, so that the move will be ready when you are, and you can stay live on your current domain with no key issues.